Exploratory Drive, Frontal Lobe Function and Adipsia in Aging

Abstract

Aging in animals in accompanied by a decrease in exploratory drive, as assessed by hole poking and spontaneous alternation tests. This decrease is caused either by increased fear of the novel testing environment (neophobia) or by apathy. Either cause may be related to dysfunction of prefrontal cortex-related pathways. The myelination of the prefrontal cortex appears late in ontogeny. In accordance to the last-in first-out principle, this brain region seems to be affected early during aging. It remains to be determined whether this decrease of exploratory behavior is reversible by behavioral intervention, by dietary changes or by the administration of psychotropic drugs. One hypothesis worth testing is whether the decrease in exploration is associated to the well-described adipsia in human aging, whose neurobiological basis has not yet been determined. It is possible to consider that the maladaptive response to thirst is responsible for some senescent changes in the brain and that reversal of adipsia by behavioral, dietary or pharmacological means improves the quality of life in the elderly.

Dehydration: Biological Considerations, Age-Related Changes, and Risk Factors in Older Adults

“…A third factor in the enhanced propensity for dehydration and alteration in water homeostasis in older adults is that the sense or perception of thirst is lessened with age (Davis and Minaker 1994;Martin and Larsen 1994). Findings consistently support the conclusion that the elderly do not become as thirsty as younger persons following water deprivation and subsequently do not drink enough to rehydrate themselves (Phillips and others 1984;Gross and others 1992;Phillips and others 1993a;Lalonde and Badescu 1995).…”

Deficits in Social Behavior Precede Cognitive Decline in Middle-Aged Mice

“…Motor activity in the open field is known to decrease in aging mice and rats (Lalonde and Badescu, 1995; Lalonde and Strazielle, 2009). Previous work (Fahlström et al, 2011) has suggested that locomotion decline in middle-aged mice is exclusively associated with exploratory tasks, even when animals have been analyzed over longer time periods.…”

Neurobehavioral evaluation of high blood pressure and low blood pressure mice

“…By contrast, the spontaneous alternation rate of old controls was not above chance. Since no alternation was observed even at the shortest retention interval, this result implies an age-associated defect in exploratory tendencies (Lalonde & Badescu, 1995), rather than in memory.…”